core: add Ref()/Unref() bus calls for units

This adds two (privileged) bus calls Ref() and Unref() to the Unit interface.
The two calls may be used by clients to pin a unit into memory, so that various
runtime properties aren't flushed out by the automatic GC. This is necessary
to permit clients to race-freely acquire runtime results (such as process exit
status/code or accumulated CPU time) on successful service termination.

Ref() and Unref() are fully recursive, hence act like the usual reference
counting concept in C. Taking a reference is a privileged operation, as this
allows pinning units into memory which consumes resources.

Transient units may also gain a reference at the time of creation, via the new
AddRef property (that is only defined for transient units at the time of
creation).

1 files changed, 13 insertions, 14 deletions

diff --git a/src/core/manager.c b/src/core/manager.c
index 7576d038a2..b58f68fa7a 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -1287,10 +1287,11 @@ int manager_startup(Manager *m, FILE *serialization, FDSet *fds) {
         if (q < 0 && r == 0)
                 r = q;
 
-        /* We might have deserialized the kdbus control fd, but if we
-         * didn't, then let's create the bus now. */
-        manager_connect_bus(m, !!serialization);
-        bus_track_coldplug(m, &m->subscribed, &m->deserialized_subscribed);
+        /* We might have deserialized the kdbus control fd, but if we didn't, then let's create the bus now. */
+        (void) manager_connect_bus(m, !!serialization);
+
+        (void) bus_track_coldplug(m, &m->subscribed, false, m->deserialized_subscribed);
+        m->deserialized_subscribed = strv_free(m->deserialized_subscribed);
 
         /* Third, fire things up! */
         manager_coldplug(m);
@@ -2490,7 +2491,7 @@ int manager_serialize(Manager *m, FILE *f, FDSet *fds, bool switching_root) {
                 fprintf(f, "kdbus-fd=%i\n", copy);
         }
 
-        bus_track_serialize(m->subscribed, f);
+        bus_track_serialize(m->subscribed, f, "subscribed");
 
         r = dynamic_user_serialize(m, f, fds);
         if (r < 0)
@@ -2693,15 +2694,13 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
                         manager_deserialize_uid_refs_one(m, l + 16);
                 else if (startswith(l, "destroy-ipc-gid="))
                         manager_deserialize_gid_refs_one(m, l + 16);
-                else {
-                        int k;
-
-                        k = bus_track_deserialize_item(&m->deserialized_subscribed, l);
-                        if (k < 0)
-                                log_debug_errno(k, "Failed to deserialize bus tracker object: %m");
-                        else if (k == 0)
-                                log_debug("Unknown serialization item '%s'", l);
-                }
+                else if (startswith(l, "subscribed=")) {
+
+                        if (strv_extend(&m->deserialized_subscribed, l+11) < 0)
+                                log_oom();
+
+                } else
+                        log_debug("Unknown serialization item '%s'", l);
         }
 
         for (;;) {